This invention relates to the dialysis of blood in general, and more particularly to apparatus and methods for use in the same.
A healthy kidney removes toxic wastes and excess water from the blood. In End Stage Renal Disease (xe2x80x9cESRDxe2x80x9d), or chronic kidney failure, the kidneys progressively stop performing these essential functions over a long period of time. When the kidneys fail, a patient dies within a short period of time unless that patient receives dialysis treatment for the rest of that patient""s life or undergoes transplantation of a healthy, normal kidney. Since relatively few kidneys are currently available for transplantation, the overwhelming majority of patients with ESRD receive dialysis treatment.
Hemodialysis therapy is an extracorporeal (i.e., outside the body) process which removes toxins and water from a patient""s blood. A hemodialysis machine pumps blood from the patient, through a dialyzer, and then back to the patient. The dialyzer removes the toxins and water from the blood by a membrane diffusion process. Typically, a patient with chronic kidney disease requires hemodialysis three times per week, for 3-6 hours per session. Removing blood from the body requires a vascular access to the patient""s blood system.
One common method for accessing a patient""s blood system for hemodialysis involves the use of a percutaneous catheter assembly. The percutaneous catheter assembly is inserted into a major vein, such as the femoral, subclavian or jugular vein. For long term maintenance dialysis, the jugular vein is generally the preferred insertion site. The catheter assembly is percutaneous, with one end external to the body and the other end dwelling in either the superior vena cava or the right atrium of the heart. The external portion of the catheter assembly has connectors permitting attachment of blood lines leading to and from the hemodialysis machine.
FIGS. 1 and 2 show the traditional manner of positioning a percutaneous catheter assembly 5 relative to the body. More particularly, percutaneous catheter assembly 5 generally comprises a catheter portion 10 comprising a dual-lumen catheter element 15, and a connector portion 20 comprising an extracorporeal connector element 25. The catheter assembly""s extracorporeal connector element 25 is disposed against the chest 30 of the patient, and the distal end 35 of catheter element 15 is passed into the patient""s internal jugular vein 40 (FIG. 2) and then down into the patient""s superior vena cava 45. More particularly, the distal end 35 of catheter element 15 is positioned within the patient""s superior vena cava 45 such that the mouth 50 of suction line 55, and the mouth 60 of return line 65, are both located between the patient""s right atrium 70 and the patient""s left subclavia vein 75 and right subclavia vein 80. Alternatively, the distal end 35 of catheter element 15 may be positioned so that mouth 50 of suction line 55, and mouth 60 of return line 65, are located within the patient""s right atrium 70. The percutaneous catheter assembly 5 is then left in this position relative to the body, waiting to be used during an active dialysis session.
When hemodialysis is to be performed on the patient, the catheter assembly""s extracorporeal connector element 25 is appropriately connected to a dialysis machine (not shown), i.e., suction line 55 is connected to the input port (i.e., the suction port) of the dialysis machine, and return line 65 is connected to the output port (i.e., the return port) of the dialysis machine. The dialysis machine is then activated (i.e., the dialysis machine""s blood pump is turned on and the flow rate set), whereupon the dialysis machine will withdraw relatively xe2x80x9cdirtyxe2x80x9d blood from the patient through suction line 55 and return relatively xe2x80x9ccleanxe2x80x9d blood to the patient through return line 65.
It has also been proposed to use a subcutaneous port and catheter assembly to provide vascular access for hemodialysis.
More particularly, a subcutaneous port and catheter assembly 82 is shown in FIGS. 3-5. Looking first at FIG. 3, subcutaneous port and catheter assembly 82 generally comprises a connector portion 84 comprising a subcutaneous port element 86, and the aforementioned catheter portion 10 comprising the dual-lumen catheter element 15. As noted above, the catheter element 15 in turn comprises the suction line 55 and the return line 65. Subcutaneous port element 86 includes a needle port 88 which is connected to suction line 55, and a needle port 90 which is connected to return line 65. The distal end of suction line 55 terminates in the aforementioned mouth 50, and the distal end of return line 65 terminates in the aforementioned mouth 60.
FIGS. 4 and 5 show subcutaneous port and catheter assembly 82 positioned within the body. More particularly, the assembly""s port element 86 is disposed under the skin of the patient (e.g., in the chest area of the patient), and the assembly""s catheter element 15 is passed into the patient""s internal jugular vein 40 and then down into the patient""s superior vena cava 45. The distal end of the assembly""s catheter element 15 may be positioned within the patient""s superior vena cava 45 such that mouth 50 of suction line 55, and mouth 60 of return line 65, are both located approximately between the patient""s right atrium 70 and the patient""s left subclavia vein 75 and right subclavia vein 80. Alternatively, the distal end of catheter element 15 may be positioned so that mouth 50 of suction line 55, and mouth 60 of return line 65, are located within the patient""s right atrium 70. The subcutaneous port and catheter assembly 82 is then left in this position within the body, waiting to be used during an active dialysis session.
When hemodialysis is to be performed on the patient, the assembly""s subcutaneous port element 86 is appropriately connected to a dialysis machine, i.e., needle port 88 is connected to the input port (i.e., the suction port) of the dialysis machine with an appropriate percutaneous needle (not shown), and the assembly""s needle port 90 is connected to the output port (i.e., the return port) of the dialysis machine with an appropriate percutaneous needle (not shown). The dialysis machine is then activated, whereupon it will withdraw relatively xe2x80x9cdirtyxe2x80x9d blood from the patient through suction line 55 and return relatively xe2x80x9ccleanxe2x80x9d blood to the patient through return line 65.
It will be appreciated that both percutaneous catheter assembly 5 (FIGS. 1 and 2) and subcutaneous port and catheter assembly 82 (FIGS. 3-5) comprise the catheter portion 10, which in turn comprises the dual-lumen catheter element 15, with the distal end of the catheter element normally dwelling in the patient""s vascular system.
Inasmuch as a substantial portion of catheter element 15 dwells in the patient""s vascular system (e.g., within internal jugular vein 40 and superior vena cava 45), it is desirable for the catheter element to have the smallest possible outside diameter so as to minimize interference with normal blood flow. At the same time, however, it is also desirable for the catheter element to have the largest possible inside diameter so that maximum dialysis blood flow can be achieved. Thus, from the standpoint of blood flow alone, it is desirable for the catheter element to have the thinnest possible wall thickness.
Unfortunately, however, other considerations also come into effect. For one thing, it is also important that the catheter element have the highest possible burst strength so that it will not fail when passing blood under pressure. In addition, it is also important that the catheter element be able to withstand high negative pressures without collapsing, so that blood can be withdrawn from the body at a rapid rate. Furthermore, it is important that the catheter element be capable of being bent at a substantial angle without kinking, such as, for example, at the point where the catheter element undergoes a large deflection in order to enter internal jugular vein 40 (see FIGS. 1 and 4). These and other considerations tend to significantly limit the degree to which the catheter element""s wall thickness can be reduced.
Furthermore, the choice of materials for forming the catheter element is also limited, since the element is typically deployed in the patient""s body for substantial periods of time. Currently, silicone rubber is the accepted material for forming catheter elements for use in percutaneous catheter assemblies and subcutaneous port and catheter assemblies.
The foregoing factors have, collectively, tended to limit either (1) the degree to which the outside diameter of the catheter element can be reduced, and/or (2) the degree to which the inside diameter of the catheter element can be enlarged, and/or (3) the rate at which blood can be introduced into the patient""s body through the catheter element, and/or (4) the rate at which blood can be withdrawn from the patient""s body through the catheter element, and/or (5) the degree to which the catheter element can be bent without kinking.
In U.S. Pat. No. 5,041,098, issued Aug. 20, 1991 to Loiterman et al., it was suggested that a helically wound reinforcement wire could be incorporated into the side wall of the catheter element. Such a suggestion could appear to be advantageous, since it could enable the walls of the catheter element to be made thinner yet stronger.
Unfortunately, in practice, Applicants have found that commercially-available coil-reinforced silicone rubber tubes lack the smooth interior lumen desirable for hemodialysis applications.
More particularly, Applicants have discovered that in hemodialysis applications, smooth lumen walls are important for (1) providing the laminar blood flows required for high volume blood transfer, (2) avoiding the creation of irregular blood currents and the creation of blood stagnation areas, (3) avoiding the formation of blood clots, (4) eliminating breeding areas for bacteria, and (5) facilitating flush-cleaning of the apparatus after dialysis has taken place.
Unfortunately, Applicants have also found that commercially-available coil-reinforced silicone rubber tubes lack the smooth interior lumen desirable for hemodialysis applications.
It is believed that this may be due to the facts that (1) commercially-available coil-reinforced silicone rubber tubes are generally used for purposes other than dialysis applications, and (2) the importance of smooth interior lumens has not yet been discovered by the dialysis industry.
It is also believed that commercially-available coil-reinforced silicone rubber tubes may lack the smooth interior lumen desirable for hemodialysis applications due to the manner in which such tubes are typically formed.
More particularly, it is believed that commercially-available coil-reinforced silicone rubber tubes are generally formed by (1) creating an outer tube out of silicone rubber, (2) forcing that tube open, (3) inserting the coil spring inside the forced-open silicone rubber tube, (4) releasing the outer tube so that it contracts back on the coil spring, and (5) dip molding an interior layer of silicone rubber onto the spring and the interior lumen of the outer tube. While such a process is generally adequate for capturing the coil spring within a body of silicone rubber material, it also results in an undulating interior lumen, since the process essentially covers the coil spring and the interior lumen of the outer tube with a substantially constant-thickness dip layer. Coil-reinforced silicone rubber tubes formed with the aforementioned process are not smooth enough for good hemodialysis applications.
Accordingly, one object of the present invention is to provide improved apparatus for use in the dialysis of blood.
Another object of the present invention is to provide an improved catheter element for use in the dialysis of blood, wherein the catheter element may be used in either a percutaneous catheter assembly or a subcutaneous port and catheter assembly.
And another object of the present invention is to provide an improved catheter element which has the largest possible interior diameter and the smallest possible exterior diameter, yet is resistant to bursting, collapse and kinking.
Still another object of the present invention is to provide an improved catheter element which incorporates reinforcing means within the side wall of the catheter, yet has an interior lumen which is sufficiently smooth that the catheter element may be used in hemodialysis applications with good results.
And another object of the present invention is to provide a support structure at the distal end of the catheter element to help maintain openness of the flow path through the catheter element.
Yet another object of the present invention is to provide an improved method for fabricating apparatus for use in the dialysis of blood.
And another object of the present invention is to provide an improved method for the dialysis of blood.
These and other objects are addressed by the present invention, which comprises improved apparatus for the dialysis of blood, a method for making the same, and an improved method for the dialysis of blood.
In one preferred embodiment, the present invention comprises a catheter comprising at least one flexible tubular element, the at least one tubular element having an open proximal end, an open distal end and a side wall defining a lumen extending between the open proximal end and the open distal end, the side wall (1) being formed of a biocompatible material, (2) encasing reinforcing means therein for reinforcing the side wall, and (3) having a smooth interior surface for defining the lumen, the smooth interior surface being sufficiently smooth that the at least one tubular element may be used for hemodialysis applications with good results.
In another preferred embodiment, the present invention comprises apparatus for use in the dialysis of the blood of a patient, the apparatus comprising a connector portion and a catheter portion; the connector portion comprising an outlet adapted for communication with a line connected to the input port of a dialysis machine, and an inlet adapted for communication with a line connected to the output port of a dialysis machine; and the catheter portion comprising a catheter element comprising: a suction line and a return line, each such line comprising a flexible tubular element, the tubular element having an open proximal end, an open distal end and a side wall defining a lumen extending between the open proximal end and the open distal end, the side wall (1) being formed of a biocompatible material, (2) encasing reinforcing means therein for reinforcing the side wall, and (3) having a smooth interior surface for defining the lumen, the smooth interior surface being sufficiently smooth that the tubular element may be used for hemodialysis applications with good results; the proximal end of the suction line being connected to the connector portion and in communication with the outlet, and the distal end of the suction line terminating in a suction line mouth; the proximal end of the return line being connected to the connector portion and in communication with the inlet, and the distal end of the return line terminating in a return line mouth; the suction line and the return line being adapted for disposition within the body of the patient so that the suction line mouth and the return line mouth are both disposed in the vascular system of the patient.
In yet another preferred embodiment, the present invention comprises a method for making a catheter, the method comprising the steps of: (a) providing an elongated, removable molding core; (b) forming a tubular element of biocompatible material on the molding core; (c) positioning reinforcing means for reinforcing the tubular element on the outer surface of the tubular element; (d) forming an overlayer of biocompatible material over the tubular element and the reinforcing means; and (e) removing the molding core from the coated tubular element.
In another preferred embodiment, the present invention comprises a method for the dialysis of the blood of a patient, the method comprising the steps of:
(a) providing a dialysis machine, and providing apparatus comprising a connector portion and a catheter portion; the connector portion comprising an outlet adapted for communication with a line connected to the input port of the dialysis machine, and an inlet adapted for communication with a line connected to the output port of the dialysis machine; and the catheter portion comprising a catheter element comprising: a suction line and a return line, each such line comprising a flexible tubular element, the tubular element having an open proximal end, an open distal end and a side wall defining a lumen extending between the open proximal end and the open distal end, the side wall (1) being formed of a biocompatible material, (2) encasing a reinforcing means therein for reinforcing the side wall, and (3) having a smooth interior surface for defining the lumen, the smooth interior surface being sufficiently smooth that the tubular element may be used for hemodialysis applications with good results; the proximal end of the suction line being connected to the connector portion and in communication with the outlet, and the distal end of the suction line terminating in a suction line mouth; the proximal end of the return line being connected to the connector portion and in communication with the inlet, and the distal end of the return line terminating in a return line mouth; the suction line and the return line being adapted for disposition within the body of the patient so that the suction line mouth and the return line mouth are both disposed in the vascular system of the patient;
(b) placing the suction line mouth and the return line mouth in the vascular system of the patient;
(c) connecting the outlet to the input port of the dialysis machine, and connecting the inlet to the output port of the dialysis machine; and
(d) operating the dialysis machine.